Petroleum pitch competes with coal tar pitch in many applications where the pitch is used as a carbon source and/or as a binder. The critical properties that are evaluated when deciding what type of pitch to use include: (a) flow properties, as measured by softening point and/or viscosity, and (b) carbon yield, as measured by ASTM D 2488, Coking Value by Modified Conradson Carbon.
Another pitch property that is also becoming of increasing interest is the polycyclic aromatic hydrocarbon content. The U.S. Pat. No. 5,746,906 patent describes a coal tar pitch having a low polycyclic aromatic hydrocarbon content and a method of making such pitch where a high softening point coal tar pitch (softening point of 120-175° C.) was mixed with a low softening point petroleum pitch to make a binder pitch having a softening point of 107-114° C. and a polycyclic aromatic hydrocarbon content slightly above 15,000 ppm.
In the manufacture of coal tar pitch, if more low boiling point materials are left in the pitch product, the resulting product has a lower softening point and a lower viscosity. In the case of petroleum pitch manufacturing, a high softening point petroleum pitch can be “cut back” with a hydrocarbon liquid material to produce a petroleum pitch having a lower softening point and a lower viscosity at a given temperature. It has long been understood in the industry, that a relationship between the softening point and viscosity exists (i.e., if one were lowered, the other would be lowered also).
Generally speaking, for a given softening point/viscosity, a petroleum pitch will have a lower carbon yield than a coal tar pitch. However, despite a potentially lower carbon yield, petroleum pitch offers certain advantages over coal tar pitch. One advantage that petroleum pitch has over coal tar pitch is the significantly lower concentration of solids of the petroleum pitch material. It is desired in the industry to fine a way to improve the flow properties (i.e., decrease the softening point and viscosity) with minimum effect on the carbon yield of petroleum pitch.
In the past, many types of materials have been used to modify the flow properties of such petroleum products as pitch and asphalt. Historically, these have been petroleum based, non-oxygenated hydrocarbons such as diesel fuel or various types of fuel oils, kerosene or various cutback oils. However, the use of these solvent “cutback” materials often has a dramatic effect on the carbon yield of the petroleum pitch and may cause problems with flash point due to increased volatility of the final product.
Examples of viscosity modification of bituminous materials include the use of a fluoro or chlorofluoro derivative of lower alkanes, such as disclosed in Smith et al., U.S. Pat. No. 4,151,003. The halogen content of the final product is a concern. The viscosity of the heavy hydrocarbons is significantly cut by the halogens to allow transport of the heavy hydrocarbons such as by pipeline. However, the presence of halogens in the final product causes other problems unless the halogenated material is removed. In contrast, the viscosity modification of the present invention does not have this problem.
Still other methods include reducing the viscosity of heavy hydrocarbon oils by preheating a stream of heavy carbon hydrocarbon oil in a stream of gas, mixing under pressure, and passing through a nozzle to form fine oil droplets such that a strong shearing action is created as the heavy oil and gas are forced through an orifice, as described in Dawson et al. U.S. Pat. No. 5,096,566.
In other situations, such as hydrocarbon/water emulsions, various viscosity modified emulsions are described. For example, the Schilling U.S. Pat. No. 5,320,671 describes mixing a bituminous emulsion aggregate slurry with a cationic emulsifier prepared as a reaction process of a polyamine with polycarboxylic acid hydrides and a kraft lignin. Other emulsions are described in the Schilling U.S. Pat. No. 5,328,505, Holleran, U.S. Pat. No. 5,474,607, and Krivohlavek, U.S. Pat. No. 5,834,359. Still other dispersant/emulsions are described in Wallace, U.S. Pat. No. 2,686,728; Ljusberg-Wahren, U.S. Pat. No. 4,957,511; McDonald, U.S. Pat. No. 4,085,078; Haire et al., U.S. Pat. No. 4,877,513 (also generally described in the abstract Haire, B. UNITAR 5th International Conference (Caracas 8/4-9/91) Proceedings V2, 121-126 (1991)); and Ohzeki et al., U.S. Pat. No. 4,539,012.
While these references describe viscosity reduction of emulsions, such references are not be considered applicable to the current invention since the viscosity reduction disclosed herein is for neat hydrocarbons, not a hydrocarbon/water emulsion.
Therefore, there is a need to produce a viscosity modifier that is useful with petroleum pitches, but does not have the above described drawbacks associated with the viscosity modifiers currently in use.
In particular, there is a need for a viscosity modifier that provides improved characteristics to the pitch and the pitch end product.
There is a further need for a viscosity modifier useful with heavy hydrocarbons which provides improved safety features such as low volatility and low toxicity. In specific examples, i.e., petroleum pitch, there is a need for viscosity modification without having a significant effect on carbon yield.
Recently, the use of biodiesels, such as methyl esters of fatty acids derived from either soybean or animal fats have received some attention to augment diesel fuel supplies in the United States. Until the present invention, however, no one had thought to use oxygenated compounds, specifically esters, more specifically methyl esters and even more particular, biodiesel, as a viscosity reduction agent for heavy hydrocarbons regardless or origin, including, in particular, petroleum based hydrocarbons such as asphalt cements and petroleum pitch as well as coal tar derived heavy hydrocarbons.